Bit depth & sampling rates

Most audio file formats use a variety of bit depth and sample rates

Bit depth

16, 24 and 32 

Sampling rate

44.100Hz, 48.000Hz, 96.000Hz and 192.000Hz

48k is common for video

16 bit  44.100Hz    standard for CD

Sample Rate & Pulse Code Modulation (PCM)

PCM   encodes audio waveform as a series of amplitudes in the time

           domain. The sampling takes place at precise regular intervals

           controlled by a quartz crystal clock.

           For successful recording the sample rate must exceed 40 kHz,

           that’s why audio CDs have a sampling rate of 44.1 kHz.

           However 48 kHz is the standard sampling rate for broadcasting.

Analogue to digital

To enable computers and hard disk recorders to record and edit sounds,

those sounds must be digitized.

Digitized audio is a series of “snapshots” that we hear as countinuous sound.

     

                           Analog signal                                Resulting sampled signal

Sample rate defines the number of samples per second measured in kHz

The more samples there are, the higher the quality.

BIT DEPTH         limits quantities such as  dynamic range  and  signal-to-noise ratio

wide dynamic range

For  each 1-bit increase in bit depth, the dynamic range will increase by 6 dB.

24-bit digital audio has a maximum dynamic range of 144 dB.

16-bit maximum dynamic range is 96dB.

Bit depth is only meaningful when applied to pure PCM (Pulse-code modulation)devices.
MP3 and other lossy formats are non-PCM formats

SAMPLE RATE   limits the  frequency

AC3

AC3 is a compression system used by Dolby which produces excellent  

results.

AC3 uses “temporal or psychoacoustic masking” to compress the

signal by a ratio of about 12:1 in comparison with the original recording.

AC3 compresses a multichannel signal down to two tracks and is normally

used to encode audio on a variety of formats, such as DVD, Digital TV and

Dolby Digital Film prints.